Wellhead and seal arrangement



Nov. 18, 1969 M, HOLBERT, JR.. ET AL WELLHEAD AND SEAL ARRANGEMENT n 5 R d Y 1 my m a c w m Wm H A m l m 4 a 8 6 4 8 m 1 a j w a 6 z 3 4 /0 Z z. f d F 22 F 7 1 L 0 Z a; 3 v M J y 0 m w m Nov. 18, 1969 HOLBERT, JR" ET AL 3,478,822

WELLHEAD AND SEAL ARRANGEMENT Filed May 15, 1968 2 Sheets-Sheet 2 United States Patent 3,478,822 WELLHEAD AND SEAL ARRANGEMENT Marvin L. Holbert, Jr., and John Slack, Houston, Tex.,

assignors to Gray Tool Company, Houston, Tex., a corporation of Texas Filed May 15, 1968, Ser. No. 732,802 Int. Cl. E21b 33/03 U.S. Cl. 166-88 8 Claims ABSTRACT OF THE DISCLOSURE For sealing the annulus between the head. bore and a hanger, two rubber axially spaced seal rings are provided having an expanding unit mounted between them. O-rings seal the expanding unit to the head bore and hanger. The expanding unit comprises a fluid actuated, double acting piston having a circumferential slip, actuated upon extension of the pistons, to maintain the two seal rings compressed.

Background of the invention In order to assist in maintaining control of a well, during drilling thereof and to seal the annulus exteriorly of a casing from the bore of the casing or the annulus between the casing bore and the next inner string of well conduit, it has become conventional to provide annular sealing elements of various types.

Procedures for the setting of these conventional seals often require manipulation of setting devices from closeat-hand positions, or with visual checking. Obviously, such procedures are ill-adapted to be used in underwater drilling and in other instances where it is not possible or not desirable (even in on-land installations) to conduct well completion operations from close proximity to the wellhead.

Summary of the invention The present invention provides means for establishing a circumferential seal in an annulus between the exterior of one element and'the bore of another, which incluces provision of axially spaced, resiliently compressible seal rings and a fluid pressure actuated device forcible simultaneously toward both rings,frorn between then, to compress the rings. The latter device incldes a latch mechanism for holding the sealing rings in resiliently compressed, sealing condition even after the device-actuating fluid pressure is relaxed.

Brief description of the drawings The principles of the invention will be further hereinafter discussed with reference to the drawings wherein preferred embodiments are shown. The specifics illustrated in the drawings are intended to exemplify, rather than limit, aspects of the invention as defined in theclaims.

In the drawings: v

FIGURE 1 is an elevation view of a partly completed wellhead with one longitudinal quadrant cut-away and sectioned, showing a sealing arrangement according to a preferred embodiment of the invention, about to be actuated.

FIGURE 2 is a longitudinal sectional view on a larger scale of the sealing arrangement of FIGURE 1.

FIGURE 3 is a sectional view similar to FIGURE 2 of a second embodiment. I

In FIGURE 1, a well is shown at a stage wherein a casing head 12 mounted on a casing string 14 is already the wellhead to the platform at the surface, that the head 12 and casing string 14 would be lowered through the conductor pipe to support on the wellhead and that temporary plugs initially installed in the side outlets of the casing head would be removed and conventional valves and conduits conventionally connected to the side outlets. When the first string or casing has been cemented, the conductor pipe may be replaced by a blowout preventer stack 11 and riser extending from the stack to the surface. The BOP stack and riser may remain in place during the subsequent operations as described below, when using the type of wellhead elements shown in the drawings.)

The casing head 12 includes side outlets 16 and 18 communicating with its generally cylindrical rthroughbore 20. The bore 20 is preferably of slightly smaller diameter than the bore of the BOP stack. A pawl actuating groove 22 and snap ring seat groove 24 are shown provided for seating and supporting a hanger 26 as fully explained in the copending US. patent application of Pitts et al., Ser. No. 539,242, filed February 18, 1966, now US. patent 3,405,763, issued Oct. 15, 1968. Suffice it to say here, by way of summary, that the ring 28 is split so as to be of C-shape and is initially held by a pin arrangement (not shown) in radially contracted condition within the groove 8. As the hanger 26 with its supported casing string 30 is lowered into the bore of the head 12, past its final seating level, then lifted somewhat, a pawl on the pin arrangement trips in the groove 22, allowing the ring 28 to expand and move to the position shown in FIGURE 1, upon lowering of the hanger again. Thus the ring 28 rests on the seat 32 in the head and supports the hanger 26 via the downwardly facing circumferential seat 34 on the exterior of the hanger. Longitudinal flutes 36 on the hanger 26 exterior permit communication between the casing string annulus 38 and the side outlets 16 (for instance to facilitate cementing operations).

In the embodiment of FIGURE 1, the head 12 is shown being a compact head, meaning that the hanger 26 seats low in the head, leaving room in the head bore above the hanger 26 for receiving (at a later stage of completion than that shown) another hanger, for instancea tubing hanger, to be supported on seat 40 the upward extension 42 of the hanger 26. The extension 42 is provided with a radial port 43 at the level of the side outlets 18 whereby communication is provided between the bore of the casing string 30 and the outlets 18.

The hanger 26, above its seat 34, is cylindrically reduced in external diameter from 44 to 46 to provide a recess 48. The hanger 26 then extends upwardly at 42 at its greater diameter, which is slightly smaller than that of the head 12 throughbore. For convenience in manufacturing, the extension 42 may comprise a separate part, as shown, for instance threadably secured to the upper end of the remainder of the hanger 26 at 50.

It should now be noticed that about intermediate between the upwardly, outwardly facing frustoconical axially lower surface 52 of the recess 48, and the downwardly outwardly facing frustoconical axially upper surface 54 thereof, at least one, and preferably severalangularly spaced radial ports 56 are provided communicating between the bore 58 of the hanger 26 and the exterior of the hanger 26 within the recess 48.

Starting from the axially lower end thereof, the recess 48 is shown receiving a first sealing ring 60, a double acting piston device 62 and a second sealing ring 64. The sealing rings and 64 are of resiliently compressible material, such as neoprene rubber and are shown being of rectangular section, having an inner diameter when relaxed, approximating that of the radially inner floor of the recess 48 and an outer diameter when relaxed approximately equal to that of the outside of the hanger 26 above and below the recess 48. When at rest, as shown in FIG- URE 1, the upper ring 64 is adjacent the top of the recess, the lower ring 60 is adjacent the bottom of the recess and the device 62 occupies the space axially between the two sealing rings, with its lower surface 66 abutting the axially facing upper surface 68 (i.e. the back) of the lower ring 60 and its upper surface 70 abutting the axially facing lowed surface 72 (i.e. the back) of the upper ring 64.

The double acting piston, ring compressing and locking device 62 includes a first annular piston 76 having a downwardly and outwardly facing frustoconical axially lower surface 66, a generally cylindrical radially inner surface 78, a generally cylindrical radially outer surface 80 and an axially upwardly facing upper end 82 shown terminating near or below the level of communication of the ports 56 with the recess 48. Near the lower end 66, the inner surface 78 is of approximately the same diameter as the radially inner floor of the recess 48 and is provided with a radially inwardly opening, circumferential recess 83 which receives an O-ring 84 for providing a rolling seal between the hanger 26, within the recess 48, and the first piston 76. Somewhat above the recess 83, the surface 78 is radially relieved to the upper end 82 in order to minimize the area of contact with the hanger. Near the lower end 66, the outer surface 80 is of about the same diameter as the hanger 26 exterior above and below the recess 48. Somewhat above the level of the lower end 66 (for instance near the level of the O-ring 82), the surface 80 undergoes a radial reduction in diameter to provide an annular, axially upwardly facing shoulder 86.

The reduction in diameter of the surface 80 continues to the upper end 82. Near the upper end 82, the surface 80 is provided with a radially outwardly opening, circumferential recess 88 which receives an O-ring 90 for providing a rolling seal between the exterior of the first annu ar piston 76 and the interior of a second annular piston 92 of the device 62. Axially intermediate the reduction in diameter of the surface 80 and the recess 88, the surface 80 is shown provided with another radially outwardly opening circumferential groove 94 for receiving a latch or slip 96. As shown (FIGURE 2), the groove 94 has an axially upwardly facing lower surface, a radially outwardly facing inner surface and an outwardly and downwardly facing frustoconical upper surface. The slip ring 96 is preferably made of a hard, yet elastic, steeel, such as A181 410 stainless steel. The slip ring lower, radially inner and upper surfaces generally conform to those of the groove 94 except that the upper surface thereof, when the slip ring is free, protrudes upwardly and outwardly at least slightly (for instance approximately inch) beyond the upper surface of the groove 94. Thus the slip ring radially outer surface, when the slip ring is free, increases slightly in diameter between the lower and upper extents thereof. At its lower end, the diameter of the slip ring is substantially equal to the radial depth of the groove 94. The slip ring 96 may be split so as to be mounted in the groove 94 after manufacture.

The second piston 92 has an upwardly and outwardly facing frustoconical axially upper surface 70, a generally cylindrical radially inner surface 98, a generally cylindrical radially outer surface 100, and an axially downwardly facing lower end 102. Near the uppper end 70, the inner surface 98 is of approximately the same diameter as the radially inner floor of the recess 48 and is provided with a radially inwardly opening, circumferential recess 104 which receives an O-ring 106 for providing a rolling seal between the hanger 26, within the recess 48 above the ports 56 and the second piston. Somewhat below the recess 104, the surface 98 is radially reduced in a diameter to the lower end 102 in order to provide a downwardly facing shoulder 108, located somewhat above the level of the ports 56. The reduced-diameter portion 110 of the internal surface 98 of the second piston is sealingly engaged by the O-ring 90 and in stressed circumferential line contact with the nose of the slip ring 96. The second piston in its region of reduced thickness is sufiiciently thin that it may be initially made somewhat oversize, slid over the exterior of the first piston until the second piston lower end 102 abuts the first piston exterior shoulder 86, then radially contracted to the shape shown, for instance by a forging operation such as rolling or swaging.

The particular slip ring arrangement shown constitutes a preferred embodiment; modifications will occur to those skilled in the art. For instance the'slip ring and groove therefore may be modified so as to'have the relative configurations shown for the ring and groove in FIGURES 25 of the copending US. patent application of Quebe et a1. Ser. No. 553,245, filed May 26, 1966.

In FIGURE 1, there is also shown a combination packoff energizer and test plug device 112 (shown in its energizing position). In order to energize the seals 60, 64 the device 112 is lowered into the bore of the hanger 26, for instance on the lower end of a string of drill pipe 114 to which it is threadably secured at 116. The device 112 includes a core or block 118 and an annular sleeve 120 mounted circumferentially on the exterior of the block for limited axial movement thereon. The block 118 has an axially upwardly opening socket 122 therein which communicates with the bore 124 of the string of drill pipe 114. One, or sevenal angularly spaced radial ports 126 in the block communicate between the socket 122 and the exterior of the block, opening into a circumferential, radially outwardly opening groove 128 in the block. One, or a plurality of angularly spaced longitudinal flutes 130 lie athwart the groove 128, having lower ends at 134 and upper ends at 136. At 138, above the level of the groove 128, the exterior'of the block is provided with an upper, circumferential, axially downwardly facing shoulder. Likewise, at 140, below the level of the groove 128, the exterior of the block is provided with a lower, circumferential, axially upwardly facing shoulder. The latter is shown being defined on an annular ring 142 threadably mounted at 144 on the lower end of the exterior ofthe block to allow the sleeve to he slipped onto the block and the ring 142 then threaded onto the block to mount the sleeve 120 on the block for limited axial movement between the surfaces 138, 140.

The sleeve 120' has an outwardly and downwardly facing annular shoulder 146 defined thereon which mates with a corresponding internal, circumferential seat 148 formed in the bore of the hanger 26 to accurately axially position the sleeve 120 relative to the hanger 26. The exterior of the sleeve 120 is shown provided with a radially outwardly opening circumferential groove 150 in communication with' the radial ports 56. The internal surface of the sleeve 120 is also shown provided with a radially inwardly opening circumferential groove 152 at the level of the groove 150, one, or several angularly spaced radial ports 154'formed through the sleeve 120, communicating between the grooves 150 and 152. Above and below the external groove 150, the sleeve 120 is circumferentially grooved at 156 and 158 to. receive 0- rings 160. and 162, respectively, which seal between the exterior of thesleeve 120 above and below thegroove 150 and the bore of the casing hanger 26 above and below the ports 56 to. establish fluid tight communication between the outer ends of theports 154 and the inner ends of the ports 56..Above andbelow the internal groove 152, the sleeve .120 is circumferential-1y grooved at 163, 1 64 toreceive O-rings 166and,168,,respectively, whichseal between the bore of the sleeve 120 above and below the groove 152 .and the external surface-of, the block 118. The sleeve 120 internal surfaceis also shown providedwith a further internal, circumferential groove 170 above the level of the groove 164, near the upper extent of the sleeve 120. The groove 170 receives an O- ring 172 for sealing bet-ween the bore of the sleeve 120 and the exterior of the block 118; v 1

It should now be noticed that when the paths just described are in the position shown in FIGURE 1 (i.e. with the sleeve 120 supported at a predetermined level in the head, for instance upon the hanger 26 as shown, and the block lowered until its upper, downwardly facing shoulder is supported at a predetermined level, for instance by abutting the upper end of the sleeve 120 as shown), there is a continuous, fluid tight passageway from the bore 124 of the drill string 114, through the socket 122, ports 126, groove 12-8, flutes 130 (passing under the O-ring 166'), the groove '152, the ports 154, the groove 150 and the ports 56, and into the space 174 between the upwardly facing rear shoulder on the lower, first piston and the downwardly facing rear shoulder on the upper, second piston. With these elements in their FIGURE 1 positions, pressure applied through the drill string bore, passing through the passageway just recapitulated, can be employed to force the first and second pistons 76, 92 axially away from one another. This causes axial compression of the seal rings 60', 64 and their radial expansion into stressed sealing engagement between the exterior of the hanger 26 and the bore of the head 12. During the seal energizing step, the slip 96 protruding radially outer surface acts on an inclined plane, allowing slippage of the second piston radial inner surface relatively upward. However, once the seal rings 69 and 64 have been energized as desired, fluid pressure on the pistons may be relaxed, as the nose 176 on the slip ring 96 will engage the second piston radially inner surface (FIGURE 2) in a sense to prevent retraction of the first and second pistons toward one another.

If the alternative slip ring arrangement described in above-mentioned U.S. patent application Ser. No. 553,245 is used the latch mechanism operates somewhat differently as explained more fully therein, but similarly allows extension and prevents retraction.

In order to test the effectiveness of sealing, the drill string and block 118 may be raised, for instance about two inches in the embodiment shown, until the upwardly facing, lower shoulder on the block 118 abuts the bottom of the sleeve 120. When in this position, a continuous, fluid-tight passageway is established through the bore of the drill string 114, the socket 122, the ports 1'26, groove 128, flutes 130 (passing under the O-ring 172) and the annulus between the hanger 26 and head 12. Upon closing valve means in the conduits leading from the side outlets 16 and opening the valve means in the conduits leading from the scale outlets 18, the integrity of the seals at 60, 64 may be tested, by applying fluid pressure through the bore of the drill string 114 and monitoring upstream of the seals 60, 64 (for instance at the upper end of the drill string bore) for a pressure drop and/or downstream of the seals 60, 64 (for instance in the conduit leading from one of the side outlets 18) for a pressure rise. If leakage is detected, the drill string and block 118 may be lowered to the first-described position, further pressur applied to the first and second pistons, and the pressure test repeated. Upon completion of testing, the drill string, block and sleeve may be withdrawn upwardly from the well through the blowout preventers and further drilling or completion conducted for instance to allow landing of another casing or tubing hanger and its supported string to be supported on the upper end of the hanger 26 upward extension within the head 26, for instance as shown and further described in the U.S. patent of Pierce, Jr., 3,354,962, issued Nov. 28, 1967. With the provision of combined hanger hold down and support means as described in the U.S. patent of Pierce, 3,248,132 issued Apr. 26, 1966, the further hanger could be supported on such support means, as described therein. Thus it should be apparent that wells completed using the equipment described herein, may be drilled and the casings set and cemented with one blowout preventer setup, for instance, as described in the U.S. patents of Hynes, 3,289,765, issued Dec. 6, 1966 and 3,336,978, issued Aug. 22, 1967.

In certain circumstances, it may be preferred or desirable to energize the casing hanger to casing head bore seals fiom externally of the head. In FIGURE 3, a modification to permit this is shown. Elements thereof which correspond to elements in the embodiment of FIGURES 1 and 2 are correspondingly numbered and provided with subscripts a. In FIGURE 3, the head 12a, at a level intermediate the lower outlets 18 and seat 32 the head is stretched and provided with a radially inwardly opening recess 48a which receives a first sealing ring 60a, a double-acting piston device 62a, and a second sealing ring 64a. Stretching of the head and hanger shown is desirable to avoid interfering with running of the hanger and setting the ring 28 (shown in FIGURE 2). The longitudinal radial section of the device 62a generally mirrors that of the device 62 so that the space 1740 between the upwardly facing shoulder 82a on the first piston and the downwardly facing shoulder 108a on the second piston opens radially outwardly toward the bore of the head 12a. A radial part 200 through the head 12a opens into this interpiston space. Fluid pressure may be applied to the first and second piston shoulders to energize the seals 60a and 64a, through the conduit 202 leading from the port 200 to the drilling platform, into sealing engagement with the hanger 26a. With the side outlets 16 closed and the side outlets 18 opened (as described in respect to FIGURES 1 and 2) pressure in the line 202 may be monitored for a pressure drop indicating leakage past the seals 60a, 64a.

Familiar terms of spatial orientation such as up and down or similar ones used in this specification describe preferred, usual orientation of the devices under discussion. They are used to convey the relevant concepts most expeditiously, and are not intended to exclude inversion, canting, recumbency or other varied spatial orientation of the devices described, unless the need for a particular orientation is evident.

I It should now be apparent that the wellhead seal arrangement as described hereinabove possesses each of the attributes set forth in the specification under the heading Summary of the Invention hereinbefore. Because the wellhead seal arrangement of the invention can be modified to some extent without departing from the principles of the invention as they have been outlined and explained in this specification, the present invention should be understood as encompassing all such modifications as are within the spirit and scope of the following claims.

What is claimed is:

1. Apparatus for sealing the annulus between a first, radially inner part having a generally cylindrical exterior peripheral surface, and a second, radially outer part having a generally cylindrical internal surface surrounding the exterior peripheral surface on said first part, comprising:

means defining a circumferential groove in one of said parts, said groove opening radially toward the other of said parts;

said groove having means defining a generally axially upwardly facing lower surface, a generally axially downwardly facing upper surface and a radially facing floor extending between said lower and upper surfaces: a first resilient annular seal ring received in said groove adjacent said floor and said lower surface and extending toward adjacency with said other part; a second resilient annular seal ring received in said groove adjacent said floor and said upper surface and extending toward adjacency with said other part; means defining a lateral opening through one of said first, radially inner part and said second, radially outer part, into said annulus at a level intermediate said first and second resilient annular seal rings; an annular seal ring expanding and locking device received in said groove axially between said first and second resilient annular seal rings;

said expanding and locking device including: a first an- Said means defining a longitudinal thronghbol'e through nular piston having an axially lower surface arranged Said hanger; to engage said first resilient annular seal ring axially said second lateral outlet being in communication with rearwardly of the latter; d ng throughbore- 'a second annular piston having an axially upper surface e apparatus of claim 4 wherein said generally arranged to engage said second resilient annular seal Cylindrical internal Surface f Said head defines the P ring axially rearwardly f th l tt riphery of a longitudinal throughbore for said head;

means defining an axially upwardly facing surface on a d hanger having an upper end located below the said first piston in communication with said lateral upper extent of said head throughbo opening; 10 means received between said head and said hanger,

means defining an axially downwardly facing surface on pp r Said hanger on said head Within 331d said second piston in communication with said lateral head throughbore; opening; means defining a lateral part through said hanger, beresilient means providing a circumferential seal between low the upper end th and said first piston, axially intermediate said axially lowmeans defining an upwardly facing additional hanger er and said axially upwardly facing surfaces thereof, at On aid hanger near said upper end thereof, and the part having said lateral opening therethrough; above said lateral part through said hanger; resilient means providing a circumferential seal between whereby, upon receipt of an additional hanger on said said second piston, axially intermediate said axially additional hanger seat, said second lateral outlet upper and said axially downwardly facing surfaces will remain in communication with the throughbore thereof, and the part having said lateral opening there of said hanger through said last-mentioned lateral through; and part.

slip means engaging said first and second pistons, said 6, The apparatus of claim 5 wherein said lateral openslip means being constructed and arranged to permit ing through one of said first, radially inner part and said axial movement of said first and second pistons away Second, radially Outer P Proceeds through Said hanger from one another and to prevent axial movement of and said apparatus further comprises a combination packsaid first and second pistons toward one another, off energizer and test plug received in said hanger throughwhereby upon admission of pressurized fluid to said bore and including: a generally cylindrical body having annulus between said first piston axially upwardly means defining a socket opening through the upper end facing surface and said second piston axially downthereof; wardly facing surface through said lateral opening, means on said body for securing said body to the lower said first and second pistons axially compress and radially expand said first and second resilient annular seal rings into sealing engagement between said first,

movement of the first and second pistons toward one another. 3. The apparatus of claim 2 further including resilient end of a conduit string with said socket in communication with the bore of the conduit string; a tubular sleeve circumferentially surrounding said body radially inner part and said second, radially outer intermediate the axial extent of said body; part, and said slip means retain said first and second means defining an upper and a lower stop on said pistons forced against said axially compressed, radialbody, positionend to alternately engage said sleeve ly expanded first and second resilient annular seal for limiting axial movement of said body with respect r ng to said sleeve between a first, lower position and a 2. The apparatus of claim 1 further including means second, upper position; defining a circumferential groove in one of said first and means defining a first lateral fluid passageway through second pistons, opening radially the part having said said sleeve intermediate the ends thereof; lateral opening; resilient means sealing between said sleeve and said means defining a tubular sleeve on the other of said first hanger throughbore above and below said first laterand second pistons co-extending with said one of said al fluid passageway and placing said first lateral fluid first and second pistons axially past said groove on passageway in fluid tight communication with said said one of said first and second pistons; lateral opening through said hanger; said slip means including a slip ring received in the lastmeans defining a second lateral fluid passageway mentioned groove and extending radially therefrom through said body, communicating between said for engagement with aid sleeve; socket and the exterior of said body radially under said slip having a generally frustoconical radial surface Said Sleeve;

thereof terminating at the larger diameter end thereof resilient means sealing between said sleeve and said in a sharp circumferential nose engaging said sleeve body for: for permitting axial movement of the first and second (a) placing said second lateral fluid passageway pistons away from one another and preventing axial in fluid tight Communication With Said first eral fluid passageway and out of communication with said annulus above said second resilient seal ring when said body is in the first,

means providing a circumferential seal between the piston having said last-mentioned groove and said sleeve, axially intermediate said last-mentioned groove and said axially upper end of said first piston.

lower position thereof, whereby said first and second resilient seal rings may be axially com pressed and radially expanded by pressurized fluid entering said device via said body socket,

4. The apparatus of claim 1 wherein a well conduit and for string hanger constitutes said first, radially inner part and (b) placing said second lateral fluid passageway wherein a head for said hanger constitutes said second, in fluid tight communication with said annulus radially outer part; and

wherein said apparatus further comprises: means providing at least one first lateral outlet on said head into the annulus between said hanger and said head, below said first and second'resilient annular seal rings;

means providing at least one second lateral outlet on said head into the annulus between said hanger and said head, above said first and second resilient annular seal rings;

above said second resilient seal ring and out of communication with said first lateral fluid passageway when said body is in the second, upper position thereof, whereby integrity of sealing provided by said first and second resilient seal rings may be tested after axial compression and radial expansion thereof. 7. The apparatus of claim 6, wherein the resilient means sealing between said sleeve and said body comprises:

a first O-ring received in means defining a first circumferential radially inwardly opening groove in said sleeve, below said second lateral fluid passagey;

a second O-ring received in means defining a second circumferential radially inwardly opening groove in said sleeve, above said second lateral fluid passageway; and

a third O-ring received in means defining a third circumferential radially inwardly opening groove in said sleeve above and axially spaced from said second circumferential radially inwardly opening groove;

said apparatus further comprising means defining at least one longitudinal flute in said body in communication intermediate the ends thereof with said second lateral fluid passageway;

said flute, when said body is in said first position thereof, extending axially below said second O-ring and terminating axially short of said first and third rings;

said flute, when said body is in said second position thereof, extending axially above said third O-ring and terminating axially short of said first and second O-rings.

8. Apparatus for establishing a circumferential seal in an annulus between the cylindrical exterior of one element and the bore of another element, comprising:

two axially spaced resiliently compressible-expansible seal rings and a fluid pressure actuated device circumferentially received in said annulus with said device axially between said two rings;

shoulder means in said annulus on axially outer sides of said rings, restraining axial movement of said rings;

means for communicating fluid pressure to said device for forcing said device simultaneously axially toward both rings from between them to axially compress and radially expand said rings into sealing contact with both the exterior of said one element and the bore of said other element; and

latch means on said device for holding the sealing rings in resiliently axially compressed, radially expanded sealing condition even after relaxation of deviceactuating fluid pressure.

References Cited UNITED STATES PATENTS 3,155,401 11/1964 Musolf 166-88 X 3,255,823 6/1966 Barton 16688 X 3,268,243 8/1966 Word 16689 X 3,311,168 3/1967 Pierce l6689 3,336,978 8/1967 Hynes 166-21 3,354,962 11/1967 Pierce 16689 NILE C. BYERS, JR., Primary Examiner US. Cl. X.R. 

